As one of causes which generate noise in a pneumatic tire, there is cavity resonance noise due to air with which an inside of the tire is filled. This cavity resonance noise is generated due to vibration of air inside the tire, the vibration being caused by vibration of a tread portion because the tread portion vibrates due to irregularities of a road surface.
As a method of reducing noise caused by a cavity resonance phenomenon as described above, there has been proposed one where a time period during which resonance occurs at the same resonance frequency is reduced by changing, along a circumferential direction of the tire, in a cross-sectional area of a closed space formed with a tire and a wheel (for example, refer to Patent Document 1). More specifically, in order to change the cross-sectional area of the closed space, a bulkhead having a predetermined volume is installed onto an inner surface of the tire, or onto an outer peripheral surface of a rim.
In the abovementioned method, however, if a change in cross-sectional area of the closed space is made large for the purpose of increasing an effect in cavity resonance noise reduction, the bulkhead interferes with deformation of the tire in some cases, and rim assembling workability is deteriorated in some cases. Therefore, a size of the bulkhead is restricted, and it is difficult to increase the effect in cavity resonance noise reduction.
[Patent Document 1] Japanese patent application Kokai publication No. 2001-113902